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68_Mag

Engine help desperately needed

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68_Mag
Guys, I know you're all growing weary of my non-Simplicity/ AC tractor posts. But if you can help me now, I'll not bother you again. I have an 18 horse Briggs and Stratton opposed 2 cylinder engine. The carb and fuel pump have been professionally rebuilt. New coil, flywheel clean. I had it starting last night by shooting some starter fluid into the carb, but it died like it wasnt pulling gas through. So today I cleaned out all my fuel lines and replaced the filter. I pulled the line off the fuel pump and gas ran through, so I put it back on. However, it refuses to start now even on starter fluid. I put my hand over the top of the carb and turned it over, it pulls air in then pushes air out. I then moved my thumb to a spark plug hole, and it's the same deal- air in, air out. However, with both plugs removed, turning the engine over doesnt cause any gasoline mist to come out. It's like it isnt getting gas, which shouldnt be possible. The man who rebuilt my carb/ pump has been doing this work for 50 years and now just sells parts, except in extreme cases. All told, I'm 300 dollars in debt trying to make this thing run and driv,e and almost frustrated to the point that if someone offered me 50 bucks for it I'd take it. I dont know what's left to do...I need some help.

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Mel_W
It sounds like the fuel solonoid isn't opening up to let the fuel to the main jet in the carb. Look on the side of the carb there should be a wire on a round thing make sure it is getting power or it won't open. this is there to stop the gas when you turn off the key so it won't backfire. if you get power and it still won't start take the solonoid out and plug the hole, it will run till you get a replacement.

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UCD
The valve timeing is off. It should only suck on the carb side and not blow back. With the plug out it should only blow out not suck back in. That tells me that the valve timeing is off. On the intake stroke the exhust valve should be closed and the intake valve open causeing a suction on the carb. On compression stroke both valves should be closed causeing air to blow out the plug hole with the plug removed. On the combustion stroke both valves are closed. on the exhust stroke intake valve is closed, exhust valve is open With either of these valves open or closed at the wrong time will cause a blow back at the carb. and a suction on the sparkplug hole.

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arjr111
You can check the fuel pump flow by removing the fuel line from the fuel pump to the carb. and cranking the engine. There may be gunk in the tank the fuel lines may be clogged. BTW, if you can get it to run by squirting something into the carb. that would indicate a fuel problem.

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68_Mag
Okay, here's my carb deal- there are two lines to the pump. One is from the tank, the other goes into the crankcase. A breather, maybe? The pump is directly mounted on the carb.

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BLT
quote:
Originally posted by 68_Mag
Okay, here's my carb deal- there are two lines to the pump. One is from the tank, the other goes into the crankcase. A breather, maybe? The pump is directly mounted on the carb.
Have you in stalled a pump rebuild kit? The diaprams might be hard and non fuctional. I don't know if those parts are included in carb rebuild kit. Pump has three lines, one from tank, one to carb and the one to the crankcase makes the diaphrams function to pump the gas.

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BLT
quote:
Originally posted by 68_Mag
I can post a picture tommorrow, but unless I'm missing something there are only two line- attaching places on the pump.
Sorry I frogot you have a carb mounted pump, only two lines then. Then it sounds more like a stuck valve.

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tractormike
If you have access to a compression tester that would give you a better idea on what's going on with the piston and valves. If you use a compression tester, try both cylinders and get a reading. Then put about 1/2 of an ounce of motor oil in each cylinder and take the readings again. If the second readings are quite a bit higher the piston rings may be bad. With poor compression the engine may not create enough suction to suck gas into it. How did the engine run before or didn't run and you are trying to get it going? Just something else to try.

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arjr111
Another way to check a fuel flow problem, (which, I think it is, if you can start it by squirting gas into the carb.) is to connect an old (clean) tank and line directly to the carb. I keep old plastic ones from junkers.--Let gravity feed the fuel in. If it starts and runs good, you have a fuel flow problem.

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UCD
quote:
Originally posted by 68_Mag
I put my hand over the top of the carb and turned it over, it pulls air in then pushes air out. I then moved my thumb to a spark plug hole, and it's the same deal- air in, air out.
If there is air blowing out the carb that is a valve/timeing problem nothing else. You can spray all the starting fluid you want if there is no compression and it is blowing out the carb it will not fire. If it was just a fuel problem it would fire on the starting fluid. Al Eden is one of the resident EXPERTS here and if you can't belive him who can you believe

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68_Mag
Okay, thanks guys. I'll get a compression test, but I'm going to agree with Al and say it's valves. Since I have no idea how to adjust or work with valves, I'll take it to a gentleman I saw today- he'll do the entire valve system for 70 bucks. Thanks!

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Al
Hi, A couple of thoughts. If this mower has been mowing at 1/2 or about throttle, or has some plugged fins there is a good chance that a valve seat has come loose. Check and see if a seat is loose in the block and can be moved by hand when the valve is off the seat. In Brs school they stress that loose seats are caused by these two reasons. Something I forgot to mention. Good luck, Al Eden

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